Derivatized Rhodamine dye and its copolymers

ABSTRACT

Disclosed are the Rhodamine B esters of hydroxy C 2  -C 6  lower alkyl acrylates. Specifically, the hydroxy lower alkyl radical is a linear hydroxy lower alkyl radical having the hydroxy group attached to the terminal carbon atom. Also shown are copolymers of diallyldimetyl ammonium chloride which contains from 0.01-2 mole percent of these Rhodamine B esters and their use in treating industrial waters.

This is a divisional of U.S. Ser. No. 08/975,886, filed Nov. 21, 1997,now U.S. Pat. No. 5,808,103, which is a divisional of U.S. Ser. No.08/682,497, filed Jul. 17, 1996, now U.S. Pat. No. 5,772,894.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to Rhodamine B which is modified to contain avinyl group and its incorporation into radically polymerized compoundssuch as diallyldimenthyammonium chloride (DADMAC) polymers.

2. Description of the Prior Art

Technological advances have made it economically practical to monitorthe residual level of polymeric coagulants in wastewater effluents.Knowledge of the fate of coagulants has several advantages:

1) monitor treated water residuals,

2) control coagulant addition, and

3) elucidate coagulation mechanisms.

This allows better control of dosage levels of these coagulants and tominimize these polymers contributing to pollution. A common approach tomonitoring the level of water soluble polymer coagulants has been, toblend fluorescent dyes in small amounts and to use fluorescence of themixture to determine the concentration of the polymer in aqueoussystems.

This approach has met with some success but it has limitations. In usingsimple blends of fluorescent dyes with polymeric coagulants there is theproblem that the dye associates itself with other components, such asparticulates. Subsequent fluorescent detection of the dye does notprovide the location of the polymeric coagulant. A more recent approachhas been to covalantly modify the dye so that it might be incorporatedby means of chemical reaction into the polymer. Since the dye and thecoagulant are physically attached, detection of the dye also detects thecoagulant polymer. While this approach has met with some success, it iseconomically important that the dye be readily detected at lowconcentrations. Particularly there is not presently available a DADMACpolymer which contains chemically combined therewith a fluorescent dyesuitable for monitoring these polymers when they are used in aqueoussystems.

If it were possible to modify polymers with a highly fluorescent dye, sothat the dye became a part of the molecule and that the so modifiedpolymer could be readily detected in the part per billion (ppb) rangeusing existing fluorescent detection techniques, an advance in the artwould be afforded. Also of importance would be, to use in themodification of the polymers, a dye which was easily synthesized fromavailable chemicals, was stable and retained a high degree offluorescence. Finally, the modified polymer should have activity as awater treating chemical corresponding to the activity of a similarunmodified polymer.

SUMMARY OF THE INVENTION

The invention comprises the Rhodamine B ester of a hydroxy C₂ -C₆ loweralkyl acrylate. The hydroxy lower alkyl radical preferably, is a linearhydroxy lower alkyl radical having the hydroxy group attached to theterminal carbon atom. In another preferred embodiment, the Rhodamine Bester is a hydroxy lower alkyl radical is a C₂ -C₄ radical, an exampleof which is the Rhodamine B ester of 4-hydroxybutyl acrylate. Theimportant point is that the hydrocarbon linkage contain a hydroxy groupand an acrylate group. The hydroxy group for modification of RhodamineB, and the acrylate group for free radical polymeric incorporation.

The invention also comprises copolymers of diallyldimetyl ammoniumchloride which contains from 0.01-2 mole percent of the Rhodamine Besters of the types described above. It is noted that any free radicalpolymerization process could incorporate the invention as long as thedye's fluorescent properties were retained. The invention furthercontemplates using these polymers in water treating applications suchas, but not limited to, coagulation. This allows the dosage and residualquantities of the polymers to be controlled and monitored usingconventional fluorescence detecting equipment even though the polymersare present in the ppb range.

THE DRAWINGS

FIG. 1 shows a scheme for reacting Rhodamine B with 4-hydroxy butylacrylate.

FIG. 2 illustrates the polymerization of DADMAC with the modifiedRhodamine B of FIG. 1.

FIG. 3 demonstrates the ability of a DADMAC-Rhodamine B copolymer to actas a coagulant and be easily detectable at low dosages.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Modified Rhodamine B and its DADMAC Copolymers

Rhodamine B is a well known fluorescent dye with its structure beingshown in FIG. 1. 4-hydroxy butyl acrylate is a well known acrylate esterand is commercially available. While this ester is preferred otheracrylate esters that may be used in the practice of the invention are2-hydroxy ethyl acrylate and 6-hydroxy hexyl acrylate and the like. Thehydroxy acrylate esters are desirably reacted with the carboxylic acidgroup of the Rhodamine B at low temperatures such at about roomtemperature ±24 degrees C. using the synthetic methods generallydescribed in the publications: Tetrahedron Letters No. 46 pp 4775-8,Pergamon Press, 1978 and Euro Polymer J. Vol. 27 No. 10 pp 1045 and1048. The disclosures of these references are incorporated herein byreference.

The DADMAC polymers modified by the acrylate ester modified Rhodamine Bmay be synthesized using known free radical polymerization techniques.These copolymers may contain between 0.01 to 2 mole percent of themodified Rhodamine B monomer based on DADMAC. Of course, the inventionis in and or itself, a monomer and potentially could be incorporated athigher levels. Preferably the amount of the fluorescent monomer iswithin the range of 0.1 to 1 mole percent. The modified or tagged DADMACpolymers have an intrinsic viscosity, as measured in 1M NaNo₃ at 30degrees C., of at least 0.3. For most water treating applications suchas coagulation the intrinsic viscosity should be within the range of 0.3to 0.9. For some applications the intrinsic viscosity may be 1.6 orgreater. When used to treat industrial waters the dosage of the modifiedpolymers would usually vary from a few parts per million up to severalhundred depending on the system treated and the intrinsic viscosity ofthe polymer used. When used as a coagulant the dosage would typically bebetween a few ppm up to ca. 100 ppm.

EVALUATION OF THE INVENTION

Synthetic Procedure: 4-Hydroxybutylacrylate/Rhodamine B Ester

The following procedure was used to prepare this material in thelaboratory and is shown in FIG. 1. To a 100 mL round bottom flask,equipped with a magnetic stirring bar, was added 3.00 g (6.26 mole) ofRhodamine B (97%) and 40 mL of anhydrous methylene chloride solvent. Themixture was stirred, under nitrogen, until the Rhodamine reagent wasdissolved. An amount (0.08 g, 0.65 mole) of 4-dimethylaminopyridine(DMAP) was then added to the flask, along with 1.5 mL (1.6 equivalents)of 4-hydroxybutylacrylate (HBA, 96%). The mixture was then cooled to 0degrees C., and 6.26 mL of 1,3-dicyclohexylcarbodiimide (DCC, 1.0 Msolution in methylene chloride, 1 equivalent) was injected into thereaction flask with stirring. The reaction was held at 0 degrees C. for1/2 hour, then the reaction was allowed to slowly warm to roomtemperature, and then stirred under nitrogen overnight. It was notedthat the reaction by-product dicyclohexylurea (DCU) began to precipitatefrom solution shortly (approximately 3 minutes) after the addition ofthe DCC.

At the end of the reaction period the methylene chloride solvent wasremoved via rotary evaporation, and the reaction mixture re-dissolved in50 mL of acetonitrile. The insoluble DCU was filtered off and thesolvent removed and the product dried under a vacuum, leaving anamorphous solid, that is soluble in water and most polar organicsolvents. The product also has the characteristic of an extremelypowerful dye. Some impurities were removed by passing the materialthrough a silica gel plug (70-270 mesh) using an acetonitrile mobilephase. In this way 1.6 g of the dye was isolated (molecular wt.=605.19amu). Thin layer chromatography (TLC) showed the presence of threespots, two are weak and one is strong. The strong spot corresponds tothe product. A weak spot below the product spot corresponds to unreactedRhodamine B. A weak spot above the product spot is unknown, it may bedue to dimerized product. All the spots seemed to be fluorescent. TheTLC solvent that gave the best separation was isopropyl alcohol. NMRanalysis gave rise to complex spectra that indicated that the esterproduct was formed. The purity was approximately 90%. The majorimpurities were approximately 5% unreacted Rhodamine B reagent and 5% ofan unknown compound.

Synthetic Procedure: Tagged DADMAC Polymer

The following laboratory method was used to prepare a DADMAC polymercontaining the above Rhodamine acrylate dye monomer and is shown in FIG.2. Into a 250 mL reaction kettle equipped with a stirring shaft,thermocouple, condenser, nitrogen inlet, and an addition port, was added0.28 g (0.13 mole percent based on monomer) of the dye monomer(approximately 90% pure) and 5.16 g D.I. water. To this was added 80.64g of a 62.0% DADMAC monomer solution. The mixture was stirred and purgedwith nitrogen. A quantity of 18.0 g of NaCl was added to the mixture andthe reaction mixture heated to 58 degrees C. in a water bath. Aninitiator solution was prepared by dissolving 0.50 g of V-50 initiatorinto 5.00 g of D.I. water. One mL of this initiator solution was theninjected into the reactor, and a timer was started. After one houranother 1 mL portion of the initiator solution was added to the reactor,and again at the two hour and three hour mark. At this point the mixturewas a very thick paste. After 4.5 hours the polymer began to climb upthe stirring shaft. When the timer reached 5 hours, 40 mL of D.I. waterwas added to the mixture, then an additional 17 mL of water was added at5.25 hours. The reaction temperature was then raised to 80 degrees C.,and the remaining 1 mL of the initiator solution was injected into thereactor. The mixture was then held at 80 degrees C. with stirring forone hour. The reactor was removed from the water bath and 83 g of D.I.water was added with stirring. The mixture was allowed to cool andanother 83 g of water was added to the reactor to give a 15% polymersolution. The product produced was a viscous dark pink material.

The following procedures were used to characterize the polymer. TheBrookfield viscosity was obtained using a #2 spindle at a speed of 12.The intrinsic viscosity (I.V.) was taken on a 1% polymer solutionprepared from 6.67 g of polymer product, 50 mL of 2M NaNO3, 1 mL of 1Msodium acetate solution, and diluted to 100 mL with D.I. water. Dialysisexperiments were performed using a 12,000-14,000 MW cut-off membrane.Standard techniques were employed. The polymer product was precipitatedand isolated by adding a small amount of the product to a large volumeof acetone. The resulting gel was isolated and dissolved in a smallamount of methanol. Any insoluble solids were filtered off, and themethanol polymer solution added to a large volume of acetone. Theprecipitated polymer was collected, washed, and dried under a vacuum.The dye monomer was incorporated into the dye at 0.13 mole percent(based on DADMAC monomer, assuming a dye monomer purity of 90%), or0.08% by weight of product. About 99% incorporation of the dye into thepolymer was achieved. Total polymer solids of the tagged polyDADMAC wasmeasured at 15%. The synthesized tagged polymer had the followingcharacteristics setforth in Table I.

                  TABLE I                                                         ______________________________________                                                     Tagged pDADMAC                                                                            pDADMAC                                              ______________________________________                                        Appearance:    Deep Red/Pink Color                                                                         Clear White                                        Brookfield Viscosity: 1363 cps 990 cps                                        I.V.: 1.0 dL/g 1.03 dL/g                                                      pH: 4.85 4.68                                                                 Wt. Average MW: 890,000 475,000                                               Number Average MW: 70,000 32,000                                              Polydispersity: 12.7 14.8                                                     Polymer Solids: 15% (theo.) 14.97                                           ______________________________________                                    

Except for the color, tagged pDADMAC has similar characteristics toun-tagged pDADMAC. PolyDADMAC dye incorporation was determinedanalytically. The polymer remained colored after precipitation andwashing. The polymer was also placed in a 12,000-14,000 dialysismembrane and dialyzed with D.I. water for 48 hours. Only a small amountof color was observer to pass out of the membrane. The material in themembrane was bright pink. A control experiment was done, in which, thedye monomer was blended with a sample of un-tagged pDADMAC. In this casepractically all of the dye seemed to pass through the membrane leavingthe un-tagged polymer behind. Analysis indicated that there were about 9ppm of residual tagged monomer in the tagged polymer.

Detection Limits

Lower detection limits are desirable for several reasons. Lowerdetection limits allows formulators to use lower dye levels in newproducts. For control purposes, a dye-tagged molecule requires detectionwithout changing product properties. Finally, for tagged polymerdetection, the higher the dye molecule fluorescence sensitivity, thelower the detection limit. This last point is important for answeringthe question of polymer residuals in treated waters. Fluorescencesensitivity is defined as:

    Fluorescence Sensitivity=extinction coefficient×Quantum Yield

From Table II it is shown the modified Rhodamine has a higherFluorescence Sensitivity than Rhodamine B. By modifying Rhodamine B weget two distinct advantages over Rhodamine B: high fluorencencesensitivity and the ability to incorporate the dye into free-radicalpolymerization reactions. For tagged pDADMAC, the detection limit wasdetermined to be 50 ppb using standard fluorometry techniques. It couldbe as low as 10 ppb.

                  TABLE II                                                        ______________________________________                                                         Extinction                                                     Absorption Coefficient Relative Quantum                                       Peak (nm) (1-mol/cm) Yield*                                                 ______________________________________                                        Rhodamine B                                                                             555        110,000    0.62 (absolute)                                 Modified 560 88,500 0.96                                                      Rhodamine B                                                                   Tagged 585 181 0.425                                                          polyDADMAC                                                                  ______________________________________                                         *Rhodamine B has an absolute Quantum yield of 0.62.                      

Stability

Since the Rhodamine B modified polymers is formed by free radicalpolymerization via chemical reaction of an acrylate onto thecarboxphenyl moiety, the reverse hydrolysis reaction would remove thedye moiety. Consequently, the acrylate group's stability to hydrolysisis important. The modified Rhodamine B-acrylate monomer was subjected topotential hydrolysis conditions and using chromatography to determinethe free Rhodamine B (residual and from hydrolysis), the monomer, andany other hydrolysis products. Results showed that at pH 7 and lowmonomer concentration (1-20 ppm), about 15-20% of the tagged monomerwere hydrolyzed after 28 days at room temperature without exposure tolight. However, high monomer concentration (800 ppm) solution appearedto be stable up to 4 weeks at room temperature without exposure tolight. It is predicted that the dye monomer's hydrolysis rate will beslower when it is attached to a polymer, due to possible stericconstraints.

Tagged Polymer Activity

Aeration Basin effluent wastewater from a refinery was used for activitytesting. FIG. 3 shows that tagged polyDADMAC has activity. This resultproves that chemically tagging pDADMAC does not inhibit coagulationpower. Activity was measured in NTUs (Nephrolytic Turbidity Units).

We claim:
 1. A copolymer of diallyldimethyl ammonium chloride whichcontains from 0.01-2 mole percent of the Rhodamine B ester of a hydroxyC₂ -C₆ lower alkyl acrylate.
 2. The copolymer of claim 1 wherein thealkyl of the hydroxy C₂ -C₆ lower alkyl is linear and the hydroxy isattached to the terminal carbon atom.
 3. The copolymer of claim 1 wherethe Rhodamine B ester is the ester of a hydroxy C₂ -C₄ lower alkylacrylate.
 4. The copolymer of claim 1 where the Rhodamine B ester is theester of 4-hydroxybutyl acrylate.